Knowledge Base

Secure Remote Password (SRP)

The Transport Layer Security Secure Remote Password^[502] cipher suite^[471][472]s provide secure communication by establishing key exchange^[467] based on one or more party's knowledge of a password, using a Secure Remote Password^{[391][392][393]} which is an augmented Password-authenticated key agreement^[415][416] protocol. Some cipher suites verify authenticity^{[201][202][203]} of the parties only by SRP while others use it together with public-key cryptography^{[346][347][348]}. The algorithm is considered secure ^[282][283], but leading client applications do not use this algorithm. Unless your application or requirements specifically call for their use, it is generally safer to avoid cipher suites that are not adopted and supported by a critical mass of the industry.

If your application or requirements specifically call for the use of algorithms which are not used by the leading client applications set the cipher suite order explicitly and cipher suites used by the leading client applications be preferred over the ones which do not used by them.

Digital Signature Standard (DSS)

Digital Signature Algorithm^{[83][84][85][86][87][88]} is a digital signature^{[231][232][233][234]} algorithm, which is considered secure^[500][501], but leading client applications do not use this algorithm. Unless your application or requirements specifically call for their use, it is generally safer to avoid cipher suites that are not adopted and supported by a critical mass of the industry.

Remove the cipher suite from the list of cipher suites supported by your server.

AES-128

Encryption algorithm Advanced Encryption Standard^{[169][170][171][172][173][174][175][176]} is a block cipher^{[524][525][526][527]} for which there is no known practical attack that would allow the attacker to recover the encrypted text without knowledge of the key when the algorithm is implemented correctly. However improper implementations may lead to a side-channel attack^{[106][107][108]} as it has happened in case of OpenSSL^{[519][520] [161][162][163]}.

Prefer cipher suites with greater key size of AES (eg: perfer AES-256 over AES-128).

Cipher Block Chaining (CBC)

Encryption mode is cipher block chaining^{[132][133][134]}. It is vulnerable^[103] to timing attack^[479] (eg: Lucky Thirteen attack^[331][332]) and padding oracle attack^{[45][46][47][48]} (eg: POODLE attack^{[362][363][364]}).

Remove the cipher suite from the list of cipher suites supported by your server or at least set the cipher suite order explicitly and any cipher suite modes be preferred over ciphers suites with CBC modes.

128

The symmetric key^{[193][194][195]} withkey size^[438] more than 128 bits as it is should be according to National Institute of Standards and Technology^[428][429] so it is not vulnerable to preimage attack^[215] and it cannreliably prove that message came from the stated sender (its authenticity) and has not been changed, so connection is not open for a man-in-the-middle attack^[414].

Remove the cipher suite from the list of cipher suites supported by your server.

128

The block cipher^{[524][525][526][527]} uses a block size^[409] larger than 64 bits, so it is not vulnerable to sweet32 attack^{[496][497][498][499]}.

SHA-1

message authentication code^{[128][129][130][131]} is a hashed message authentication code^{[418][419][420][421][422][423][424]} which is considered secure^[159], despite the fact that the underlayingcryptographic hash function^{[510][511][512][513]} (Secure Hash Algorithm 1^{[204][205][206]}) is considered insecure^{[370][371][372][373][374][375][376]}.

If your application or requirements specifically call for the use of a message authentication code^{[128][129][130][131]} that does not provide authenticated encryption^[563] prefer block cipher mode of operation^{[293][294][295][296][297]} (eg: counter with CBC-MAC^{[266][267][268]}, Galois/Counter Mode^{[65][66][67][68]} or message authentication code^{[128][129][130][131]} (eg: Poly1305^[289][290]) that proved authenticated encryption over the ones which does not provide it. In case of a hashed message authentication code^{[418][419][420][421][422][423][424]} prefer message authentication code^{[128][129][130][131]} based on Secure Hash Algorithm 2^[71][72][73] over the ones based on Secure Hash Algorithm 1^{[204][205][206]}.